* Changes for adding support for matchedDN parsing

[koushik2506]

Hi,
So here is a PR for #177.
I have a added a NewErrorWithDN function in errors.go which creates a Error object with MatchedDN populated.
Corresponding changes to pass on this error in operations
Added a test in ldap_test with a search on a wrong base to print out the matchedDN error.

[vetinari]

I would just change this and drop NewErrorWithDN() to have this PR only go into the upcoming v3... @liggitt what do you think?

[koushik2506]

The Error structure, gets a MatchedDN populated, only if the values returned by getLDAPResultCode() is put into it. If you drop NewErrorWithDN(), then NewError() would have to take 3 arguments. This would make code blocks like:

packetResponse, ok := <-msgCtx.responses
if !ok {
    return NewError(ErrorNetwork, errors.New("ldap: response channel closed")
}

Needing an empty string argument for MatchedDN.

Can we make getLDAPResultCode into something like GetLDAPError which will return the full Error object and do a err != nil check. So places like this:

if packet.Children[1].Tag == ApplicationAddResponse {
    resultCode, resultDescription, matchedDN := getLDAPResultCode(packet)
    if resultCode != 0 {
        return NewErrorWithDN(resultCode, errors.New(resultDescription), matchedDN)
    }
 }

Would become

if packet.Children[1].Tag == ApplicationAddResponse {
    err := GetLDAPError(packet)
    if err != nil {
        return err
    }
 }

Then we can retain NewError as is, and do away with NewErrorWithDN().

[johnweldon]

I like this suggestion - do you want to update this PR accordingly?